The invention relates to a method for monitoring the travel path of a road processing machine which drives on a base surface, a road processing machine and a system for carrying out a method for monitoring the travel path of a road processing machine driving on a base surface and the working height of a working part arranged thereon in a vertically adjustable manner.
In the construction and repair of roads and squares, machines which drive along a predetermined travel path and carry out a desired processing step are used for various operations. For example, road finishers comprising a vehicle and a smoothing board or a screeding beam fixed thereon in a vertically adjustable manner are used for applying asphalt surfaces. The asphalt material is distributed from the vehicle along the front edge of the smoothing board. When the machine advances to the prepared road bed, the smoothing board scrapes over the asphalt material and smoothes and compacts it in order to provide a continuous asphalt surface having the desired surface profile.
The prior art discloses various solutions by means of which the smoothing board can be positioned vertically so that a desired surface profile is achieved as exactly as possible. For the vertical positioning, for example, a reference is used. If, for example, a rope or a wire has to be stretched as a reference line along the road to be asphalted, this entails considerable effort. If the base surface to which the asphalt is applied is used as a reference, it must be formed very exactly with great effort. According to a further solution, a laser beam is used as a reference, in which case the height of the smoothing board relative to the laser is determined using a sensor fixed to the smoothing board, and the smoothing board is kept at a desired height.
DE 100 60 903 describes a prior art in which the position of a reference surface is determined using a sensing ski or using three laser measuring heads a distance apart in the direction of movement. In order to avoid a complicated construction for holding the laser sensors, it is proposed to arrange, at a point above the smoothing board, three differently oriented laser telemeters which determine the distance to three measuring points located one behind the other in the direction of movement. The distance values are each converted into a height and a horizontal distance. Depending on the heights determined and on the required height, a height control signal for the smoothing board or another processing tool is generated.
The accuracy of the height determination using the obliquely oriented laser telemeters is reduced by the accuracy of mounting and by the fact that at least one measuring point lies on the already applied surface. In the case of road construction machines, an exactly constant sensor orientation is scarcely achievable owing to vibrations and large temperature and humidity variations. In the case of telemeters directed obliquely forwards, a small unknown change in angle is sufficient to lead to a considerable error in the height calculated from a measurement assuming the false orientation.
U.S. Pat. No. 5,549,412 discloses a method in which a road processing machine comprising a vertically adjustable working part is used together with at least one transmitter. A sensor on the machine receives at least one signal of the at least one transmitter, and height position information which is used for the vertical positioning of the vertically adjustable working part is derived from the received signal. For example, a GPS system is used as the system comprising transmitter and sensor. In order to achieve a desired surfacing over a reference surface, the reference surface is driven over without processing merely for determining the reference surface position, which is associated with a double driving effort.
EP 1 079 029 A2 discloses a solution in which a GPS system and a tilt-adjustable rotational laser system are used for the three-dimensional control or levelling of the construction machine. The GPS system on the construction machine determines two position coordinates of the construction machine, which are communicated to the stationary rotational laser system. A required height is coordinated with the actual position coordinates, and the rotational laser is oriented so that, in the case of a linear laser receiver of the construction machine, it marks the required height. The laser receiver determines the actual deviation of the working tool from the required height. The height position of the working tool is adjusted according to this deviation. This solution is very complicated because it comprises a GPS system, a complex rotational laser system, a radio link between these systems, a linear laser receiver and at least one control. In addition, problems arise in areas, for example, under bridges, where the satellite signals required by the GPS system cannot be received.
Further possibilities for height determination of the working part are described in DE 196 47 150, in which a device and a method for controlling the installation height of a road finisher are described. The determination of the height of the screeding beam edge is effected here by potentiometer sensors, ultrasonic sensors or laser receivers.
DE 199 51 297 C1 relates to an automatic longitudinal control of a road finisher during the installation of a road layer. Solutions are used in which a prism arranged on the road finisher is followed by a total laser station. This station follows the prism by means of an optical system which can be oriented in all directions. The position of the construction machine or of the screeding beam is calculated from the solid angle of the optical system, the distance between prism and optical system and the position of the total station. For the exact height regulation of the screeding beam, the prism must be arranged as directly as possible above the rear edge of the screeding beam. However, this then results in inaccuracies in steering which adversely affect the surface profile. In order to compensate the effects of the inaccuracies in steering, parts of the screeding beam which are displaceable transversely to the travel direction are proposed, so that, even in the case of an inaccurate travel path, a precise application of the surface is ensured by an optimum lateral displacement of these parts.
A road processing machine comprising laterally displaceable screeding beam parts has a complicated mechanical design. In the case of construction machines without possibilities for lateral adjustment, the problems arising from the inaccuracy in steering persist.